1. Field of the Invention
This invention relates to cast aluminum alloys, and particularly to dimensionally stable aluminum alloy castings and to tooling fixtures therefrom.
2. Description of Related Art
Aluminum base alloys made for tooling applications are known. For example, aluminum products producers are commercially producing aluminum tooling plates with alloys containing zinc, copper, magnesium and silicon as major elements; and iron, nickel, manganese and chromium as impurities. The above materials are cast but generally are not equiaxially grained and maximum thickness availability is only 4.0 inches.
Other aluminum alloys containing zinc, copper and magnesium as major constituents (7000 aluminum series) are well known but are available only in the wrought form (hot rolled). These alloys have the typical wrought elongated and distorted grain structure that is very dense and very strong but has poor dimensional stability because of grain directionality. All wrought 7000 series aluminum alloys require a solution heat treatment, a water quench and a precipitation hardening treatment (aging) to achieve their mechanical properties.
The direct water cooled casting method is also known. It is universally used to produce aluminum billets that are subsequently worked into wrought aluminum products such as plates, bars, extrusions and forgings. It is also a well-known fact that this mechanical working of the original cast grain structure, although producing high mechanical properties after heat treatment, produces too much grain directionality to be dimensionally stable.